GASTEROPODA. 97 



tie slightly folded posteriorly ; with visible tentacula ; branchiae 

 on the fore part of the back, and covered ; anal opening placed 

 in the right side. — The posterior part of the body covered by 

 an involute shell, with neither pillar nor spire ; aperture extend- 

 ing the whole length of the shell. 



Bulla lignaria — The Wood-like Bulla. Plate XIV. fig- 

 25. Narrowed towards the top, where it is slightly umbilicated ; 

 yellowish- brown, with numerous transverse pale stria3. Two 

 inches long. Inhabits the British seas. 



Genus 9.— BULL^ A.— Zamarc^. 



Generic Character. — Body ovate-oblong, somewhat convex 

 above, and divided transversely into two parts ; the lateral lobes 

 of the foot thickened and retrousse ; head indistinct, and with- 

 out tentacula ; branchiae placed on the back.— Shell concealed 

 in the mantle ; thin, somewhat involute on one side, and desti- 

 tute of a columella or spire •, aperture large and wide. 



Bullcea aperia — The Open Bull^a. Plate XIV. fig. 23. 

 Suborbicular, pellucid, white, faintly striated, and slightly 

 wrinkled ; almost entirely open. Half an inch long. Inhabits 

 the British seas. 



Genus 10— RET USA.— Brou;n. 



Generic Character. — Animal unknown. — Shell small, oblong- 

 ovate, spiral, outer lip nearly the whole length of the body, and 

 entire ; spire very short, volutions prominent. 



Retusa pKcata.— The Plaited Retusa. Plate XIV. fig. 

 27. White, opaque, subcylindricai ; spire produced ; aperture 

 elongated, straitened at top ; two transverse plaits, and several 

 oblique ones, at the base of the columella ; outer lip thin, slightly 

 inflected. One third of an inch long. Inhabits the sea at 

 Dunbar. 



Genus 11— AKERA.— Brown. 



Generic Character. — Animal not described. — Shell elastic, 

 convoluted ; apex obtuse, canaliculated, the volutions even with 

 the body j aperture wide at the base, contracted at top, and ex- 

 I 



